Deflection During Prestressing of an Unbonded Prestressed Concrete Beam

In recent years great strides have been made towards improving the quality and strength of both concrete and steel. Reliable concrete with a compressive strength of 5000 to 12,000 psi and suitable steel with a tensile strength of over 200,000 psi can be obtained. If high strength concrete and high strength steel can be used together satisfactorily a substantial reduction in materials will result. This is partly due to the fact that the materials are stronger and partly due to the fact that dead load is reduced. In designing a plain reinforced concrete beam it is assumed that about one-third of the concrete (the part of compression ) is effective in resisting moment. The other two-thirds of the concrete serve mainly to encase the reinforcing steel in the tension portion of the beam. From the above facts it appears that much of the added expense of producing stronger concrete would be wasted. (See more in text.